Temperature Converter

About this Temperature Converter

The Temperature Converter handles the three commonly requested temperature scales: Celsius, Fahrenheit and Kelvin. Unlike most unit conversions, temperature conversion requires both multiplication and an offset, so the tool applies the correct formula for each pair.

Temperature conversions come up in cooking, weather reports, science coursework and international travel, and because the formulas involve both multiplication and an offset rather than a single fixed factor, they are more error-prone to do mentally than most unit conversions.

For related tasks, try Pressure Converter, Energy Converter or Length Converter.

How to use it

1. Enter the temperature value.
2. Choose the starting scale.
3. Choose the target scale and convert.

Practical example

0°C converts to 32°F and 273.15 K. Likewise, 100°C converts to 212°F.

A recipe calling for an oven at 180°C converts to 356°F, which is why many recipe conversion charts round it to the nearest common oven marking of 350°F for convenience.

Things to double-check

A common mistake is applying only the multiplication step of the Celsius-to-Fahrenheit formula and forgetting the +32 offset, or vice versa when converting back. Because temperature scales don't share a common zero point, both parts of the formula matter, unlike simple length or weight conversions.

The conversion formulas

To convert Celsius to Fahrenheit, multiply by 9 over 5 and add 32. To go back, subtract 32 and multiply by 5 over 9. Kelvin equals Celsius plus 273.15. Body temperature of 37 degrees Celsius is 98.6 degrees Fahrenheit and 310.15 kelvin. The two scales agree at minus 40, and water freezes at 0 Celsius or 32 Fahrenheit and boils at 100 Celsius or 212 Fahrenheit at sea level.

Cooking temperatures

Recipes use different scales depending on country. A moderate oven of 180 degrees Celsius is about 356 degrees Fahrenheit, often rounded to 350, and corresponds roughly to gas mark 4. Fan ovens run hotter, so many recipes suggest lowering the temperature by about 20 degrees Celsius. Safe cooking temperatures for meat are typically given as internal temperatures, such as 74 degrees Celsius for poultry, and a thermometer is more reliable than time.

Weather and health

A weather forecast of 30 degrees Celsius is a hot day at 86 degrees Fahrenheit, and minus 5 degrees Celsius is 23 Fahrenheit. A fever is commonly defined as a body temperature of 38 degrees Celsius, or 100.4 Fahrenheit, or higher. Check which scale a thermometer uses, especially when travelling, and note whether the reading is oral, ear or underarm, since methods differ by a few tenths of a degree.

Science and absolute temperature

Kelvin is the SI scale and begins at absolute zero, where particles have the least possible energy. Zero kelvin is minus 273.15 degrees Celsius. Scientists use kelvin for gas laws and for colour temperature, such as 6,500 K for daylight. A difference of one kelvin is the same as a difference of one degree Celsius, but one degree Fahrenheit is smaller, 5 over 9 of a kelvin, so convert differences carefully.

Quick mental estimates

For a rough Celsius to Fahrenheit conversion, double the number and add 30, so 20 degrees Celsius is about 70 Fahrenheit, while the exact answer is 68. For a rough conversion back, subtract 30 and halve, so 80 Fahrenheit is about 25 Celsius, close to the exact 26.7. The estimate works best between 0 and 30 degrees Celsius. Useful anchors are 0 Celsius for freezing, 20 to 22 Celsius for a comfortable room (68 to 72 Fahrenheit) and 37 Celsius for body temperature.

Reference temperatures

Useful anchors include a refrigerator at about 4 degrees Celsius (39.2 Fahrenheit), a freezer at minus 18 Celsius (about 0 Fahrenheit), a room at 20 to 22 Celsius (68 to 72 Fahrenheit), a hot bath at about 40 Celsius (104 Fahrenheit) and a sauna at around 80 Celsius (176 Fahrenheit). Water freezes at 0 Celsius and boils at 100 Celsius at sea level. Absolute zero is minus 273.15 Celsius, or 0 kelvin. Comparing a result with these anchors catches most errors.

Worked examples

To convert 37.5 degrees Celsius to Fahrenheit, multiply by 1.8 and add 32, which gives 99.5. To convert 350 degrees Fahrenheit to Celsius, subtract 32 and multiply by 5 over 9, which gives 176.7. Minus 10 degrees Celsius is 14 degrees Fahrenheit. A temperature of 300 kelvin is 26.85 degrees Celsius. The pattern is that the two scales have different zero points and different step sizes, so you must adjust both, which is why a simple multiplication is not enough. The converter applies the right formula for each pair.

Cooking and food safety

Recipes use different scales in different countries. Common oven settings are 160 Celsius, about 320 Fahrenheit, 180 Celsius, about 350, 200 Celsius, about 400, and 220 Celsius, about 425. Fan ovens run hotter, so many recipes suggest reducing the temperature by about 20 Celsius. Food safety guidance gives minimum internal temperatures, such as 74 Celsius or 165 Fahrenheit for poultry and 63 Celsius or 145 Fahrenheit for whole cuts of beef and pork, followed by a rest. A probe thermometer is more reliable than cooking time, since ovens and cuts vary.

Weather and health

Weather reports use Celsius in most countries and Fahrenheit in the United States. A hot day in Pakistan at 45 degrees Celsius is 113 Fahrenheit, which is dangerous for outdoor work without shade and water. A body temperature of 38 Celsius, or 100.4 Fahrenheit, is commonly taken as a fever, and below 35 Celsius, or 95 Fahrenheit, can signal hypothermia and needs medical attention. Thermometers differ in where and how they measure, so follow the instructions and use the same type when you track changes. If you are worried, speak to a doctor.

Absolute temperature and extremes

The kelvin scale starts at absolute zero, the point where particles have minimal energy, which is minus 273.15 degrees Celsius. No system can be cooled to exactly absolute zero, but laboratories come very close. Liquid nitrogen boils at minus 196 degrees Celsius, or minus 320.8 Fahrenheit, and the surface of the sun is around 5,500 degrees Celsius. Scientists use kelvin because it makes formulas for gases and radiation simple, and because a change of one kelvin equals a change of one degree Celsius. The converter helps when you move between these scales.

Key terms explained

The Celsius scale sets water's freezing point at 0 and boiling point at 100. The Fahrenheit scale sets them at 32 and 212. Kelvin starts at absolute zero and uses the same step as Celsius. Absolute zero is the lowest possible temperature, minus 273.15 degrees Celsius. Room temperature is about 20 to 22 Celsius, and normal body temperature is about 37. A thermometer measures temperature, and a probe thermometer is used for food.

Rules of thumb and quick checks

To convert Celsius to Fahrenheit, multiply by 1.8 and add 32. To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8. Kelvin is Celsius plus 273.15. The two scales meet at minus 40. A 10 degree Celsius change equals an 18 degree Fahrenheit change. Useful anchors: 0 Celsius is 32 Fahrenheit, 20 is 68, 30 is 86, 37 is 98.6 and 100 is 212.

Quick reference and sanity checks

Memorise a few fixed points. Water freezes at 0 degrees Celsius, which is 32 degrees Fahrenheit, and boils at 100 degrees Celsius, which is 212 degrees Fahrenheit at standard pressure. The two scales meet at minus 40. Room temperature of 20 to 22 degrees Celsius is about 68 to 72 degrees Fahrenheit. To convert from Celsius to Fahrenheit, multiply by 9, divide by 5 and add 32. Kelvin is Celsius plus 273.15, and absolute zero is minus 273.15 degrees Celsius. For cooking, medicine and science, check which scale an instrument shows, because a temperature difference of one degree is not the same size on both scales.

Frequently asked questions